It is possible to choose a different aspect ratios from the camera menu, e.g. 16:9, since it sometimes helps in the composition. Effectively the camera crops the live view to the desired aspect ratio (and also the JPEG files), but the full 4:3 image is always captured in the RAW files.The problem is that when such RAW file is imported to LR it appears in the aspect ratio that it was taken with, e.g. 16:9, and there's no access to the full 4:3 image.

My soluton so far is to manually modify the RAW file before importing it to LR. Specifically, I run this command: